Enhanced heat exchanger

ABSTRACT

An anti-freezing assembly includes: (a) heat exchanger for exchanging heat between a first fluid and a second fluid, the heat exchanger including: a first inlet manifold, a first outlet manifold, a second inlet manifold, and a second outlet manifold; a plurality of first flow passages, each of the plurality of first flow passages fluidly connecting the first inlet manifold to the first outlet manifold; a plurality of second flow passages, each of the plurality of second flow passages fluidly connecting the second inlet manifold to the second outlet manifold; a first porous metallic insert disposed in at least one of the plurality of second flow passages, a density of the first porous metallic insert varying in a direction of the second flow passages; wherein the first inlet manifold has a variable cross-sectional area; (b) a heater encompassing the first inlet manifold or the first outlet manifold.

CROSS-REFERENCE TO RELATED APPLICATIONS

This application claims the benefit of U.S. Provisional Application No. 62/406,855 filed on Oct. 11, 2016. This application also claims the benefit of U.S. Provisional Application No. 62/410,233 filed on Oct. 19, 2016. Both of these applications are incorporated by reference herein in their entirety.

TECHNICAL FIELD

This application relates to a heat exchanger for transferring heat between a first fluid (e.g., water) and a second fluid (e.g., refrigerant).

BACKGROUND

Existing heat exchangers are susceptible to freezing. More specifically, when water (or brine) is cooled in existing heat exchangers, the water may crystallize into ice. Ice impairs, among other things, performance of the heat exchanger by obstructing fluid flow and by weakening the structural integrity of the heat exchanger.

SUMMARY

Disclosed is a heat exchanger for exchanging heat between a first fluid and a second fluid, the heat exchanger including: a first inlet manifold, a first outlet manifold, a second inlet manifold, and a second outlet manifold; a plurality of first flow passages, each of the plurality of first flow passages fluidly connecting the first inlet manifold to the first outlet manifold; a plurality of second flow passages, each of the plurality of second flow passages fluidly connecting the second inlet manifold to the second outlet manifold; a first porous metallic insert disposed in at least one of the plurality of second flow passages, wherein a density of the first porous metallic insert varies in a direction of the second flow passages.

According to some embodiments, the first porous metallic insert is a porous metallic mesh or a porous metallic foam.

According to some embodiments, the first porous metallic insert includes a beginning portion adjacent the second inlet manifold and an end portion between the second inlet manifold and the second outlet manifold, the beginning portion having a different density than the end portion. In some embodiments, the beginning portion may have a greater density than the end portion.

According to some embodiments, the heat exchanger further includes a plurality of porous metallic inserts, the plurality of porous metallic inserts including the first porous metallic insert; wherein each of the plurality of porous metallic inserts are disposed in at least one of the plurality of second flow passages to increase structural integrity of the second flow passages and/or improve thermal performance characteristics of the second flow passages.

According to some embodiments, the heat exchanger further includes: a front cover plate and a rear cover plate; a plurality of first plates disposed in an alternating arrangement with a plurality of second plates; wherein each of the plurality of first flow passages is defined between one of the first plates and one of the second plates, each of the plurality of second flow passages is defined between one of the first plates and one of the second plates, and each of the manifolds is at least partially defined by the plurality of first plates and the plurality of second plates.

According to some embodiments, the front cover plate, the plurality of first plates, the plurality of second plates, and the rear cover plate are brazed, soldered, thermally bonded, diffusion bonded or chemically bonded together.

According to some embodiments, each of the plurality of porous metallic inserts is bonded to at least one of the first and second plates. One or more of the plurality of porous metallic inserts may be bonded by brazing, soldering, thermal bonding, diffusion bonding or chemical bonding.

According to some embodiments, each of the plurality of porous metallic inserts is brazed, soldered, thermally bonded, diffusion bonded or chemically bonded to at least two plates selected from a group consisting of the front cover plate, the rear cover plate, the plurality of first plates, and the plurality of second plates.

According to some embodiments, each of the plurality of porous metallic inserts has a beginning portion adjacent the second inlet manifold and an end portion between the second inlet manifold and the second outlet manifold, and a length between the beginning portion and the end portion, at least some of the lengths being different such that one of the plurality of porous metallic inserts is longer than at least some of the plurality of porous metallic inserts.

According to some embodiments, the heat exchanger may include a second porous metallic insert disposed in at least one of the plurality of first flow passages, wherein a density of the second porous metallic insert varies in a direction of the first flow passages, wherein the second porous metallic insert is a porous metallic mesh or a porous metallic foam.

According to some embodiments, the density of at least one of the first porous metallic inserts is different than the density of at least one of the second porous metallic inserts.

According to some embodiments, the density of one of the second porous metallic inserts is different than the density of another of the second porous metallic inserts.

According to some embodiments, the density of one of the first porous metallic inserts is different than the density of another of the first porous metallic inserts.

Disclosed is an anti-freezing assembly including: (a) a heat exchanger for exchanging heat between a first fluid and a second fluid, the heat exchanger including: a first inlet manifold, a first outlet manifold, a second inlet manifold, and a second outlet manifold; a plurality of first flow passages, each of the plurality of first flow passages fluidly connecting the first inlet manifold to the first outlet manifold; a plurality of second flow passages, each of the plurality of second flow passages fluidly connecting the second inlet manifold to the second outlet manifold; (b) a heater encompassing the first inlet manifold or the first outlet manifold.

According to some embodiments, the heater encompasses only a lower portion of said manifold.

According to some embodiments, the heat exchanger includes: a front cover plate and a rear cover plate; a plurality of first plates disposed in an alternating arrangement with a plurality of second plates; wherein each of the plurality of first flow passages is defined between one of the first plates and one of the second plates, each of the plurality of second flow passages is defined between one of the first plates and one of the second plates, and each of the manifolds is at least partially defined by the plurality of first plates and the plurality of second plates.

According to some embodiments, the heater encompasses only some of the plurality of first plates and the plurality of second plates. The heater may be configured to heat a portion of at least one of the first or second plates of the heat exchanger.

According to some embodiments, the assembly further includes a controller and a pair of differential fluid sensors configured and arranged to detect a differential pressure or temperature of the first fluid across the heat exchanger, the pair of differential fluid sensors being in operative communication with the controller. According to some embodiments, the assembly further includes a controller and a pair of fluid sensors configured and arranged to detect a pressure or temperature of the first fluid or the second fluid, the pair of fluid sensors being in operative communication with the controller.

According to some embodiments, the controller is configured to activate the heater based on the detected pressure or temperature differential. According to some embodiments, the controller is configured to activate the heater based on the detected pressure or temperature.

According to some embodiments, the controller is configured to activate the heater to heat the plurality of first plates closest to the rear cover plate to a different extent than the plurality of first plates closest to the front cover plate. The controller may be configured to activate the heater to provide a varying heat flux along the height or width or depth of the heat exchanger.

According to some embodiments, the controller is configured to activate the heater to emit a greater amount of heat near the first outlet manifold and a lesser amount of heat near the first inlet manifold.

According to some embodiments, the controller is configured to activate the heater based on the detected pressure or temperature differential indicating a presence of ice disposed in the heat exchanger. According to some embodiments, the controller is configured to activate the heater based on the detected pressure or temperature indicating a presence of ice disposed in the heat exchanger.

Disclosed is a heat exchanger for exchanging heat between a first fluid and a second fluid, the heat exchanger including: a first inlet manifold, a first outlet manifold, a second inlet manifold, and a second outlet manifold; a plurality of first flow passages, each of the plurality of first flow passages fluidly connecting the first inlet manifold to the first outlet manifold; a plurality of second flow passages, each of the plurality of second flow passages fluidly connecting the second inlet manifold to the second outlet manifold; wherein the first inlet manifold has a variable cross-sectional area to encourage uniform flow distribution and to provide free draining of the first fluid.

According to some embodiments, the heat exchanger further includes: a front cover plate and a rear cover plate; a plurality of first plates disposed in an alternating arrangement with a plurality of second plates; wherein each of the plurality of first flow passages is defined between one of the first plates and one of the second plates, each of the plurality of second flow passages is defined between one of the first plates and one of the second plates, and each of the manifolds is at least partially defined by the plurality of first plates and the plurality of second plates; wherein the cross-sectional area of the first inlet manifold is taken across a series of reference planes parallel to the plurality of first plates.

According to some embodiments, the cross-sectional area of the first inlet manifold decreases along a direction extending from the front cover plate to the rear cover plate, such that a cross-sectional area of the first inlet manifold closest to the front cover plate is greater than a cross-sectional area of the first inlet manifold closest to the rear cover plate.

According to some embodiments, the heat exchanger further includes an inclined insert disposed in the first inlet manifold, the inclined insert being shaped such that the inclined insert is flush against each of the plurality of first and second plates.

According to some embodiments, each of the first plates includes a first aperture at least partially defining the first inlet manifold, wherein the first aperture of the first plate closest to the front cover plate is larger than the first aperture of the first plate closest to the rear cover plate in the direction of the flow

According to some embodiments, each of the second plates includes a second aperture at least partially defining the first inlet manifold, wherein the second aperture of the second plate closest to the front cover plate is larger than the second aperture of the second plate closest to the rear cover plate in the direction of the flow.

According to some embodiments, at least some of the first flow passages and at least some of the second flow passages are defined by corrugations in the first and second plates, wherein at least some of the corrugations in the first and second plates include a variable corrugation pattern comprising at least one of a variable corrugation angle of attack, a variable corrugation density, and a variable corrugation width.

According to some embodiments, at least one of the first inlet manifold and the first outlet manifold are coextensively positioned with a perimeter of the heat exchanger.

An anti-freezing assembly includes: (a) heat exchanger for exchanging heat between a first fluid and a second fluid, the heat exchanger including: a first inlet manifold, a first outlet manifold, a second inlet manifold, and a second outlet manifold; a plurality of first flow passages, each of the plurality of first flow passages fluidly connecting the first inlet manifold to the first outlet manifold; a plurality of second flow passages, each of the plurality of second flow passages fluidly connecting the second inlet manifold to the second outlet manifold; a first porous metallic insert disposed in at least one of the plurality of second flow passages, a density of the first porous metallic insert varying in a direction of the second flow passages; wherein the first inlet manifold has a variable cross-sectional area; (b) a heater encompassing the first inlet manifold or the first outlet manifold.

BRIEF DESCRIPTION OF THE DRAWINGS

For a better understanding of the invention, reference may be made to embodiments shown in the following drawings. The components in the drawings are not necessarily to scale and related elements may be omitted, or in some instances proportions may have been exaggerated, so as to emphasize and clearly illustrate the novel features described herein. In addition, system components can be variously arranged, as known in the art. Further, in the drawings, like reference numerals designate corresponding parts throughout the several views.

FIG. 1 is a side view of a heat exchanger of the instant disclosure.

FIG. 2 is an isometric view of a heat exchanger of the instant disclosure.

FIG. 2a is a cross-sectional view of the heat exchanger taken along line 2 a-2 a of FIG. 2.

FIG. 3 is a front view of a first heat exchange plate.

FIG. 4 is a front view of a second heat exchange plate.

FIG. 5 is an exploded front view of a plurality of first heat exchange plates and a plurality of second heat exchange plates.

FIG. 6 is a front view of a second heat exchange plate overlaid on a first heat exchange plate.

FIG. 7 is a cross-sectional view taken along line 7-7 of FIG. 2.

FIG. 8a is a front view of a first alternative embodiment of a first heat exchange plate. FIG. 8b is a front view of a second alternative embodiment of a first heat exchange plate. FIG. 8a is a front view of a third alternative embodiment of a first heat exchange plate.

FIG. 9 is an isometric view of a heat exchanger of the instant disclosure.

FIG. 10 is a cross-sectional view of the heat exchanger taken along line 10-10 of FIG. 9.

FIG. 10a is a detail front view of a first embodiment of a water inlet manifold taken along line 10 a-10 a of the heat exchanger shown in FIG. 10. FIG. 10b is a detail front view of the first embodiment of the water inlet manifold taken along line 10 b-10 b of the heat exchanger shown in FIG. 10.

FIG. 10c is a detail front view of a second embodiment of a water inlet manifold taken along line 10 c-10 c of the heat exchanger shown in FIG. 10. FIG. 10d is a detail front view of the second embodiment of the water inlet manifold taken along line 10 d-10 d of the heat exchanger shown in FIG. 10.

FIG. 11 is an exploded front view of a plurality of first heat exchange plates and a plurality of second heat exchange plates.

FIG. 12 is a side view of one embodiment of a heater cable and an insulating member positioned on a heat exchanger.

FIG. 12a is a side view of another embodiment of a heater cable and an insulating member positioned on a heat exchanger.

FIG. 13 is a cross-sectional view of the heat exchanger taken along line 10-10 of FIG. 9 showing an embodiment of a metal mesh or metal foam.

FIG. 14 is an exploded front view of a plurality of first heat exchange plates, a plurality of second heat exchange plates, and the metal mesh or metal foam shown in FIG. 13.

FIG. 15 is a block diagram of the heat exchanger positioned to exchange heat between a vapor compression cycle circuit and a hydronic pump cycle circuit.

DETAILED DESCRIPTION

While the invention may be embodied in various forms, there are shown in the drawings, and will hereinafter be described, some exemplary and non-limiting embodiments, with the understanding that the present disclosure is to be considered an exemplification of the invention and is not intended to limit the invention to the specific embodiments illustrated.

In this application, the use of the disjunctive is intended to include the conjunctive. The use of definite or indefinite articles is not intended to indicate cardinality. In particular, a reference to “the” object or “a” and “an” object is intended to denote also one of a possible plurality of such objects. Further, the conjunction “or” may be used to convey features that are simultaneously present, as one option, and mutually exclusive alternatives as another option. In other words, the conjunction “or” should be understood to include “and/or” as one option and “either/or” as another option

FIGS. 1 to 7 illustrate a heat exchanger 10 (also referred to as HX 10). HX 10 may be any suitable heat exchanger type, such as a shell-and-tube heat exchanger or a plate heat exchanger. According to some embodiments, HX 10 is a brazed plate heat exchanger configured to exchange heat between two fluids (e.g., water W and refrigerant R) while preventing direct fluid communication or mixing between the fluids. Refrigerant may enter HX 10 at a relatively colder temperature, while water may enter HX 10 at a relatively warmer temperature. Refrigerant and water exchange heat inside HX 10 such that refrigerant leaves HX 10 at a warmer temperature or essentially the same temperature (in the latter case, when phase change occurs) and water leaves HX 10 at a colder temperature with respect to the inlet conditions for each fluid. Refrigerant and water may be arranged in counterflow in HX 10, although parallel flow is also possible, including when HX 10 is used in a reversible system such as a reversible heat pump operating in a cooling mode and in a heating mode.

With reference to FIGS. 1 and 2, HX 10 includes a front cover plate 11, a rear cover plate 14, a plurality of first heat exchange plates (referred to as first HX plates) 12 a to 12 d, and a plurality of second heat exchange plates (referred to as second HX plates) 13 a to 13 d. The front cover plate 11 and the rear cover plate 14 provide structural rigidity and an environmental barrier to the stack of first HX plates 12 a to 12 d and to the second HX plates 13 a to 13 d.

As illustrated in FIGS. 1, 2 and 2 a, one or more walls, surfaces, and/or edges of plates 11, 12, 13, and 14 cooperate to define fluid passages or apertures 15 a, 15 b, 16 a, and 16 b to convey water W and refrigerant R to and from HX 10 and to and from heat exchange passages formed between respective adjacent plates 12,13. The collection of fluid passages or apertures 15 a, 15 b, 16 a, 16 b in each plate 12,13 together serve as fluid manifolds 17. Water inlet aperture 15 a accepts water. Water outlet aperture 15 b expels water. Refrigerant inlet aperture 16 a accepts refrigerant. Refrigerant outlet aperture 16 b expels refrigerant. Respective ports 5 are connected to respective fluid manifolds 17 at front cover plate 11. It should be appreciated that fluid manifolds 17 may be configured to cooperate with either front cover plate 11 or rear cover plate 14. Fluid conduits (not shown) are connected to ports 5 and thus carry water and refrigerant to and from HX 10. It should be appreciated that the direction of refrigerant flow through HX 10 may be reversed, and although the direction of water flow through HX 10 may also be reversed, in some embodiments, the direction of water flow may not be reversed when the direction of refrigerant flow is reversed. A reversing valve comprising a 3-way or a 4-way valve may be used to reverse the flow of refrigerant in any system in which HX 10 is a part.

FIG. 3 is a front view of a representative first HX plate 12. First HX plate 12 includes circular walls, surfaces and/or edges defining apertures 15 a, 15 b, 16 a, and 16 b. First HX plate 12 is configured to include a plurality of corrugations positioned on an angle on the first HX plate 12 where the corrugations form a plurality of alternating ridges and valleys. The corrugations can be in any shape, such as sinusoidal, trapezoidal, or having the appearance of a square wave. First HX plate 12 includes a plurality of ridges 22. Sequential ridges 22 define valleys 23. When viewing first HX plate 12 from the rear, ridges 22 appear as valleys and valleys 23 appear as ridges. First HX plate 12 includes a perimeter 21. Perimeter 21 is brazed to adjacent second HX plates 13. Additionally, an alternating pair of walls, surfaces and/or edges of adjacent circular apertures (e.g., apertures 15 a,15 b or apertures 16 a,16 b) from adjacent plates 12,13 are brazed together to cause refrigerant and/or water to alternatingly flow in passages created between plates 12,13. In this way, apertures 15 a, 15 b, 16 a, and 16 b of the first HX plates 12 and second HX plates 13 define manifold 17 (see FIG. 2a ) to convey refrigerant R and water W, respectively, to and from passages formed between respective first HX plates 12 and second HX plates 13.

FIG. 4 is a front view of a representative second HX plate 13. Second HX plate 13 is similar to first HX plate 12. Second HX plate 13 is configured to include a plurality of corrugations positioned on an angle on the second HX plate 13 where the corrugations form a plurality of alternating ridges and valleys. Ridges 32 may be a mirror image of ridges 22 of first HX plate 12. Valleys 33 are defined between sequential ridges 32. If viewing the second HX plate 13 from the rear, ridges 32 appear as valleys, and valleys 33 appear as ridges. Second HX plate 13 includes a perimeter 31 brazed to adjacent first HX plates 12.

FIG. 5 is an exploded view of the front surfaces of a plurality of first HX plates 12 and a plurality of second HX plates 13. Water W and refrigerant R flow in a counterflow arrangement in passages created between adjacent plates 12,13. The water passages are positioned adjacent to the refrigerant passages to enable heat exchange between the two fluids. Water W and refrigerant R are delivered to the passages via apertures 15 a, 15 b, 16 a, and 16 b in each respective plate 12,13 that together form manifolds 17. Adjacent walls, surfaces and/or edges of apertures 15 a, 15 b, 16 a, and 16 b are brazed together in alternating fashion to cause fluid (either refrigerant or water) to be directed to passages formed between alternating pairs of plates 12,13.

For example, walls, surfaces and/or edges of water apertures 15 a,15 b on the rear surface of second HX plate 13 a are not fully brazed to the walls, surfaces and/or edges defining apertures 15 a,15 b on the front surface of first HX plate 12 b. This enables water to flow between the rear surface of second HX plate 13 a and the front surface of first HX plate 12 b.

On the other hand, walls, surfaces and/or edges defining refrigerant apertures 16 a,16 b on the rear surface of second HX plate 13 a are fully brazed to the walls, surfaces and/or edges defining refrigerant apertures 16 a,16 b on the front surface of first HX plate 12 b. This prevents refrigerant from flowing between the rear surface of second HX plate 13 a and the front surface of first HX plate 12 b.

FIG. 6 is a front view of a first HX plate 12 and a portion of a second HX plate 13 to show how ridges on forward facing surface of first HX plate 12 contact “valleys” (which appear as ridges when viewed from the rear) of the rearward facing surface of the second HX plate 13 to form nodes 61. Ridges 22 of first HX plate 12 mate with valleys 23 of an adjacent second HX plate 13 at nodes 61. Fluid passes around nodes 61. Nodes 61 may represent points where ridges 22 of first HX plates 12 are brazed to valleys 33 of second HX plates 13.

FIG. 7 is a cross-sectional view along line 7-7 of FIG. 2. Refrigerant R flows between ridges 22 of first HX plates 12 and valleys 33 of second HX plates 13. Water W flows between valleys 23 of first HX plates 12 and ridges 32 of second HX plates 13. Brazing or nodes 61 are between (a) ridges 22 and valleys 33 and (b) ridges 32 and valleys 23. It should be appreciated that the passages for water W and refrigerant R may or may not have the same geometry, surface topology, and configuration.

FIG. 8a shows a representative first HX plate 12 with apertures 15 a, 15 b, 16 a, 16 b having an outer boundary that is coextensive with perimeter 21 or at least coextensive to the outer boundary of any brazing. Because the apertures are coextensive with perimeter 21, the heat exchange area between the peripheral edges of the apertures and perimeter 21 is eliminated. As shown in FIG. 8b , the apertures may be curved such that apertures 15 a, 15 b, 16 a, and 16 b are oval-shaped or circular. As shown in FIG. 8c , only some of the apertures may be coextensive with perimeter 21. Any one or more of the apertures 15 a, 15 b, 16 a, 16 b may be coextensive with perimeter 21. Any one or more of the apertures 15 a, 15 b, 16 a, 16 b may be non-coextensive with perimeter 21. Any one or more of the apertures 15 a, 15 b, 16 a, 16 b may have any geometry, including circular, so as to be coextensive with perimeter 21. The same concepts apply to second HX plate 13. These features help prevent freezing of water W by reducing or eliminating areas of potential stagnation of water, as may occur when water flow is compromised, and to minimize, control, or eliminate heat transfer in areas around the apertures 15 a, 15 b, 16 a, 16 b.

FIG. 9 is an isometric view and FIG. 10 is a cross-sectional view taken along line 10-10 of FIG. 9 (for clarity, FIG. 10 omits views of some plates 12,13) of HX 10 in which the cross-sectional area of the water inlet manifold varies from inlet to discharge along its length, and more particularly, from its largest cross-sectional area where port 5 attaches to aperture 15 a to the smallest cross-sectional area at the discharge 95 of water inlet manifold 17 located furthest from port 5. According to some embodiments, the change in cross-sectional area equalizes flow velocity through each water passage such that the flow velocity of water in passages near front cover plate 11 is approximately equal to the flow velocity of water in passages near rear cover plate 14. According to some embodiments, the change in cross-sectional area equalizes mass flow rate through each water passage such that the mass flow rate of water in passages near front cover plate 11 is approximately equal to the mass flow rate of water in passages adjacent rear cover plate 14. By increasing flow velocity of water entering passages near rear cover plate, this configuration minimizes the likelihood of the water freezing by the time the water reaches the discharge 96 of the furthermost passages between plates 12,13 that lead to circular apertures 15 b. As stated below, varying the cross-sectional area may additionally or exclusively apply to water outlet manifold 17 to achieve essentially identical velocity and temperature change across each water flow passage (assuming that refrigerant is also uniformly distributed). Alternatively, water flow distribution across the water flow passages may be matched to the refrigerant flow distribution across the refrigerant flow passages to obtain essentially equivalent water temperature change in each water flow passage.

In some embodiments, a varying cross-sectional area from inlet to discharge of the inlet manifold 17 can be achieved by configuring HX 10 with an insert 91 positioned inside manifold 17. Without insert 91, manifold 17 has a constant cross-sectional area. With insert 91, manifold 17 has a varying cross-sectional area caused by the inclined angle of the insert 91 and resulting in flow passage 92. Insert 91 is configured to occupy a predetermined volume of manifold 17 and decrease the cross-sectional area from the inlet end of the water inlet manifold 17 to the discharge end of the water inlet manifold 17. For example, insert 91 can create a relatively large cross-sectional area at inlet 94 and a comparatively smaller cross-sectional area at discharge 95 of the water inlet manifold 17. As stated above, the same technique may be applied to water outlet manifold 17 alternatively or in addition to water inlet manifold 17. When applied to water outlet manifold 17, insert 91 may have the same configuration (i.e., insert 91 has a smaller cross-sectional area near rear cover plate 14 and a larger cross-sectional area near front cover plate 11).

Insert 91 may be a solid or hollow device positioned inside apertures 15 a. At least a portion of the outer shape of the insert may generally conform to the inner diameter of apertures 15,16. Insert 91 may also be configured at inlet 94 to have a relatively larger cross-sectional flow area than the cross-sectional flow area at the discharge 95 to increase the rate at which water flows toward the heat exchange passages positioned farthest from the water inlet port 5.

In one embodiment, insert 91 is configured as a cupped ramp on an inclined angle as shown in FIGS. 10a (inlet) and 10 b (discharge). In another embodiment, insert 91 is configured as a generally flat ramp on an inclined angle as shown in FIGS. 10c (inlet) and 10 d (discharge).

It should be appreciated that insert 91 may be a result of a subtractive manufacturing process, instead of an additive manufacturing process such that insert 91 is fully integral with and a part of plates 12,13. As stated above, according to some embodiments, insert 91 exclusively applies to aperture 15 a, corresponding to water inlet. According to other embodiments, insert 91 applies to apertures 15 a and/or apertures 15 b.

Although FIG. 10 shows the insert 91 extending across an entire length of manifold 17, it should be appreciated that insert 91 may be shorter than a length of manifold 17. According to embodiments, insert 91 begins at a plane parallel with intersecting front cover plate 11 or a plane parallel with and intersecting any one of the first and second plates 12, 13 (e.g., insert 91 may begin at any one of plates 12 a, 13 a, 12 b, 13 b, 12 c, 13 c, etc.). In addition to equalizing flow velocities, insert 91 promotes free draining of water toward port 5 and away from HX 10 when HX 10 is not in use to minimize and/or eliminate the presence of water in HX 10 that may be susceptible to freezing if HX 10 is positioned or exposed to ambient freezing conditions. According to an embodiment, insert 91 begins at a plane parallel with a leading edge of port 5, as shown in FIG. 10. When HX 10 is not in use or when water pressure ceases to be supplied to water inlet port 5, water in HX 10 flows downward under the force of gravity to water inlet manifold 17. Insert 91, by virtue of the sloped or ramped design, directs water out of water inlet port 5 and HX 10.

In other embodiments, a varying cross-sectional area from inlet to discharge of the water inlet manifold 17 can be achieved by configuring HX 10 with apertures 15 a, 15 b, 16 a, 16 b on each successive HX plate 12,13 so that the apertures progressively change in size when the HX plates 12,13 are stacked in a predetermined sequence. For example, as shown in FIG. 11, the HX plates 12,13 define larger apertures 16 b toward the inlet of manifold 17 and define progressively smaller apertures 16 b toward the discharge of manifold 17 (in the case of FIG. 11, aperture 16 b is shown by way of example as this feature is applicable also to apertures 15 a, 15 b, or 16 a). When stacked together, plates 12,13 form an aperture (e.g., aperture 16 b) having any of the geometries discussed above. The varying cross-sectional area from inlet to discharge of the water inlet manifold 17 permits free-draining of water from HX 10 as described above, but unlike above, the transition to horizontal may occur at or near the front cover plate 11 rather than at the inlet end of port 5.

FIGS. 12 and 12 a shows a heater cable 120 and an insulating member 125 positioned around at least a portion of HX 10 to reduce the likelihood of water freezing inside HX 10. Insulating member 125 may be positioned to cover one or more external surfaces of HX 10 in proximity to where freezing of water in water heat exchange passages may be anticipated. Heater cable 120 includes an electrical resistance element and may be configured to create heat upon receipt of an electrical current. Heater cable 120 may be configured to attach to the outer wall of HX 10. Insulating member 125 may include a blanket, styrofoam, rubber-like containing material or other device or material with insulating properties that may or may not be molded to conform to the outer shape of HX 10. Insulating member 125 may incorporate heater cable 120. As discussed below, heater cable 120 may include a plurality of individual heating elements.

According to some embodiments, heater cable 120 extends about water inlet manifold and/or water outlet manifold. According to some embodiments, heater cable 120 is configured to deliver a greater amount of heat to a portion of the manifold(s) nearest rear cover plate 14 and a lower amount of heat to a portion of manifolds nearest front cover plate 11.

Heater cable 120 may achieve this configuration by being more densely positioned in the area near rear cover plate 14 and being less densely positioned (or absent) in the area near front cover plate 11. It should thus be appreciated that heating provided by heater cable 120 may vary in a depth direction of HX 10 (i.e., from front cover plate 11 to rear cover plate 14). Heater cable 120 and insulating member 125 may be used in conjunction with one another, separately from one another, or in combination with any other feature disclosed herein.

As discussed below, the heating provided by heater cable 120 may vary across HX 10 such that plates 12,13 adjacent front cover plate 11 are heated to a lesser extent than plates 12,13 adjacent rear cover plate 11. As discussed above and below, such heating can be achieved by (a) increasing density of heater cable 120 adjacent rear cover plate 14 and/or (b) by controlling heating of heater elements of heater cable 120 and/or heater cable 120 to generate more heat adjacent rear cover plate 14 and less heat adjacent front cover plate 11.

Alternatively, or in addition, a density of heat delivered by heater cable 120 may vary across a length of HX 10. More specifically, heater cable 120 may deliver a greater amount of heat to the portions of plates 11, 12, 13, and/or 14 adjacent water outlet manifold 17 and a lesser amount of heat to the portions of plates 11, 12, 13, and/or 14 adjacent water inlet manifold 17. Control of heater cable 120 in the length direction may be accomplished with the techniques disclosed with reference to control of heater cable 120 in the depth direction.

According to some embodiments, heater cable 120 is more densely positioned (e.g., includes a greater number of heating elements or is more densely wound) adjacent water outlet manifold 17 and less densely positioned adjacent water inlet manifold 17. According to other embodiments, heater cable 120 has a generally constant density across a length of HX 10 (although density of heater cable 120 may still vary from front cover plate 11 to rear cover plate 14, as described above). Such a constant density configuration may be appropriate when flow of water through HX 10 is reversed.

Accordingly, the controller (discussed below), may detect a flow direction of water and cause heater cable 120 to generate a greater amount of heat at the water outlet manifold 17 and a lower amount of heat (including zero heat) at the water inlet manifold 17. According to these embodiments, heater cable 120 may have a constant density in the length direction. Alternatively, according to these embodiments, heater cable 120 may be more densely positioned at the outlet and inlet manifolds 17, and less densely positioned between the outlet and inlet manifolds 17 (e.g., in the middle of HX 10 in the length direction).

When the heat provided by heater cable 120 varies along a length of HX 10 and a depth of HX 10, a greatest amount of heat is generated at the portion of water outlet manifold 17 adjacent rear cover plate 14 and a smallest amount of heat is generated (the heat generation can be zero) at the portion of water inlet manifold 17 adjacent front cover plate 11.

FIGS. 13 and 14 show how a porous heat transfer material may be used to structurally tie adjacent HX plates together to form a stronger bond than brazing at the contact points of respective ridges from adjoining HX plates 12,13 alone. FIG. 13 is a cross-sectional view taken along line 13-13 of FIG. 2 and shows, in one embodiment, how metal mesh and/or metal foam 70 may be positioned in one or more respective refrigerant heat exchange passages.

Metal mesh and/or metal foam may extend over a complete width of the refrigerant passages such that metal mesh and/or foam extends between opposing sides of each perimeter 21, 31. Alternatively, and as shown in FIG. 14, metal mesh and/or metal foam may extend over a complete width of the portions of first and second HX plates 12, 13 including the ridges 22, 32 and valleys 23, 33 such that areas between the perimeters 21, 31 and (a) the ridges 22, 32 and (b) valleys 23, 33 do not include metal mesh and/or foam 70. According to some embodiments, metal mesh and/or foam 70 surrounds refrigerant inlet aperture 16 a such that the moment refrigerant enters a refrigerant flow passage from refrigerant inlet aperture 16 a, refrigerant encounters metal mesh and/or metal foam. Metal mesh and/or foam 70 may surround water outlet aperture 15 b to the same extent.

Metal mesh and/or metal foam 70 may be porous and configured to have a high number of apertures and surface elements per unit of area (e.g., thousands of apertures per square foot). Metal mesh or foam 70 may have varying porosity from one end of the refrigerant heat exchange passage to the other to reduce pressure drop alone the length of the passage. For example, the metal mesh and/or metal foam 70 may be more heavily concentrated in the area of the liquid refrigerant. Metal mesh and/or metal foam 70 may comprise a structured metal mesh or foam (e.g., a fixed number of mesh openings per area), or an unstructured metal mesh or foam (e.g., a nonuniform structure, at least on a microscale).

The amount, concentration or density of the porous metal mesh and/or metal foam 70 may decrease (or said another way, the porosity of the porous metal mesh and/or metal foam 70 may increase) in the area of the heat exchange passage as the refrigerant transitions to predominantly vapor from predominantly liquid thereby allowing for less pressure drop and better thermal performance of the refrigerant. In this way, an optimal balance between pressure drop and heat transfer for the refrigerant evaporating or condensing in the heat exchange passages may be achieved while also providing a large quantity of additional metal contact points for the braze to connect, beyond the number of metal contact points between adjacent ridges and valleys of adjacent HX plates 12,13, which results in a strengthened brazed heat exchanger structure.

A brazed plate heat exchanger configured in this way will be substantially more resistant to structural failure than conventional brazed plate heat exchangers should water freeze in the water heat exchange passages. The number of contact points for the braze varies according to the density of the metal mesh and/or metal foam 70 positioned in a given passageway. The velocity of refrigerant at each point over the length of the metal mesh and/or metal foam 70 may vary according to the cross-sectional area of the fluid conveying pores or apertures at each point in the length of the metal mesh and/or metal foam 70. Metal mesh and/or foam 70 may be bonded to one or more of plates 11, 12, 13, and 14 via brazing, soldering, thermal bonding, diffusion bonding or chemical bonding.

FIG. 14 shows a front view of multiple HX plates 12,13 having metal mesh and/or metal foam 70 positioned in heat exchange passages designated for conveying refrigerant. As shown in this embodiment, metal mesh and/or metal foam 70 is positioned above first plates 12 and below second plates 13. The concentration or density of metal mesh and/or metal foam 70 decreases in the direction of flow of refrigerant such that the concentration or density is greater toward refrigerant inlet aperture 16 a and lower (or non-existent) toward refrigerant outlet aperture 16 b. For example, metal mesh and/or metal foam 70 at position 70 a is denser than metal mesh and/or metal foam 70 at position 70 b, which is denser than metal mesh and/or metal foam 70 at position 70 c. It should thus be appreciated that density of metal mesh and/or metal foam 70 may vary from a beginning point adjacent to refrigerant inlet manifold 17 to an end point. The end point may be adjacent to refrigerant outlet manifold 17. According to some embodiments, and as shown in FIG. 13, the end point is between refrigerant inlet manifold 17 and refrigerant outlet manifold 17. According to various embodiments, the end point is approximately, 20, 25, 30, 35, 40, 45, 50, 55, 60, 65, 70, 75, 80, 85, or 90% of the distance between refrigerant inlet manifold 17 and refrigerant outlet manifold 17. The term approximately may correspond to a ±5, 7, or 10% tolerance.

According to some embodiments, the end point is positioned at the location where refrigerant is expected to have fully or at least partially transitioned from a liquid state into a vapor state. According to some embodiments, and as shown in FIG. 13, the end point is the same for each refrigerant passage.

Variance of the end point of successive refrigerant passages may enable the end points of the metallic meshes or foams to be positioned at the locations where refrigerant fully or at least partially transitions from a liquid state to a vapor state. According to some embodiments, the end point of refrigerant passages nearest front cover plate 11 is closer to refrigerant inlet manifold 17 and the end point of refrigerant passages nearest rear cover plate 14 is closer to refrigerant outlet manifold 17 such that the end point moves nearer to the refrigerant outlet manifold with each successive refrigerant passage (starting with the refrigerant passage nearest front cover plate 11). According to other embodiments, the end point of refrigerant passages nearest front cover 11 is closer to refrigerant outlet manifold 17 and the end point of refrigerant passages nearest rear cover plate 14 is closer to refrigerant inlet manifold 17 such that the end point moves further away from the refrigerant outlet manifold with each successive refrigerant passage (starting with the refrigerant passage nearest front cover plate 11). When each of the metal meshes or foams ends at a different location, each of the metal meshes or foams may have a different density profile along the respective refrigerant flow passages. According to these embodiments, density profiles of metal meshes or foams positioned closer to the front cover plate 11 may more quickly vary (i.e., more quickly transition from high density to low density) than metal meshes or foams positioned closer to the rear cover plate 14. Alternatively, density profiles of metal mesh or foams positioned closer to the rear cover plate 14 may more quickly vary (i.e., more quickly transition from high density to low density) than metal meshes or foams positioned closer to the front cover plate 11. According to some embodiments, shorter metal meshes or foams have a steeper density profile (i.e., more quickly transition from high density to low density) than longer metal meshes or foams.

The change in density (or porosity) of metal mesh and/or metal foam 70 is advantageous in both possible directions of refrigerant flow (i.e., metal mesh or foam 70 works when HX 10 serves as a refrigerant condenser and when HX 10 serves as a refrigerant evaporator). As described above, metal mesh and/or metal foam 70 may also be advantageous when positioned in one or more water passages to enhance structural rigidity and strength of HX 10 and therefore permit HX 10 to resist structural failure due to freezing.

The porosity of the metal mesh and/or metal foam 70 may change along the length of metal mesh and/or metal foam 70 in either a continuous or stepwise fashion. In some embodiments, various configurations of metal mesh and/or metal foam 70 may act as a substitute for corrugations between respective HX plates 12,13 to convey fluids for heat transfer purposes.

In other embodiments in which corrugated heat transfer passages are used, it should be appreciated that configuring the HX plates 12,13 with an increased number of corrugations positioned where the potential for water freezing is highest and where phase changing fluid has higher density or providing a higher angle of attack in those areas will allow for reduced cross-sectional area and additional braze contact points between adjacent HX plates 12,13, which would strengthen HX 10 and increase the margin for failure in the event of water freezing in HX 10, as well as improve thermal performance of HX 10 by providing an optimal balance between heat transfer and pressure drop characteristics as described above. Thus, HX 10 may be configured with a varying density or number of corrugations and corrugated surface topology over a given length to increase the braze contact points between adjacent HX plates 12,13 and enhance thermal performance of HX 10. The density or number of corrugations may be varied according to any of the techniques described above with reference to metal mesh or foam 70. According to some embodiments, metal mesh or foam 70 is provided in every flow passage that lacks corrugations.

FIG. 15 is a block diagram of a refrigerant circuit 6 and a water circuit 7. Refrigerant exchanges heat with water in HX 10. Compressor 1 compresses refrigerant, condenser 2 condenses refrigerant, expansion valve or capillary tube 3 expands refrigerant, HX 10 evaporates refrigerant. Pump 5 pumps water. HX 10 cools water. Heat exchanger 4 heats water. According to other embodiments, HX 10 condenses refrigerant and heats water. According to various embodiments, refrigerant circuit 6 is a heat pump circuit and includes a valve and bypass piping (not shown) for reversing flow of refrigerant through at least condenser 2 and HX 10 such that condenser 2 serves as an evaporator and HX 10 serves as a condenser. According to various embodiments, water circuit 7 (which can also be a brine circuit) may include a valve and bypass piping for reversing flow of water or brine through heat exchanger 4 and HX 10 such that heat exchanger 4 cools the water or brine and HX 10 heats the water or brine.

A controller coupled with temperature and/or pressure sensors 9 a,9 b may be used to determine temperatures and/or pressures of refrigerant in refrigerant circuit 6. A controller coupled to temperature and/or pressure sensors 9 c,9 d may be used to determine temperatures and/or pressures of water in water circuit 7. If temperatures and/or pressures of water in water circuit 7 and/or across HX 10 by sensors 9 c, 9 d indicates the presence of conditions for forming ice in HX 10, the controller may automatically and selectively activate some or all heating elements positioned on inside or outside of HX 10, such as heater cable 120 described above, to increase the temperature of the selected water heat exchange passage(s). A sudden increase in pressure in water circuit 6 and/or across HX 10 by sensors 9 c and 9 d may indicate the presence of ice or an indication of insufficient water flow through HX 10. A sudden decrease in temperature sensed at sensor 9 d with a minimal decrease in temperature sensed at sensor 9 c may indicate the presence of ice or an indication of insufficient water flow through HX 10. Any of the sensors disclosed herein may be used to measure absolute or differential temperatures or pressures at a particular location.

In one embodiment, the controller may selectively activate one or more heating elements positioned toward the rear cover plate 14 to produce more heat than heating elements positioned toward the front cover plate 11. The heating elements may be features of heater cable 120 or may be separate features. In some embodiments, the controller may be configured to selectively and dynamically adjust the duration for which the one or more heating elements are activated. For example, the heating elements positioned toward the rear cover plate 14 may be activated by the controller for a longer duration than heating elements positioned near the front cover plate 11, even if all such heating elements are initially activated at the same time. In other embodiments, the controller may be configured to activate heating elements in a progressive or staged manner to add heat as may be needed at desired locations. Thus, both activation duration and activation of heating element based on location are independent variables. If heater cable 120 is more densely positioned near end plate 14 (as described above), then separate control of individual heating elements may be unnecessary, but is still possible. Similar concepts apply to activation of heating elements across a length of HX 10 such that portions of plates 11, 12, 13, and/or 14 near water outlet manifold are heated to a greater extent than portions of plates 11, 12, 13, and/or 14 near water inlet manifold. The controller may detect temperatures and/or pressures at the water inlet and/or outlet manifolds via sensors 9 c and 9 d. The controller may also be programmed to activate/deactivate one or more features described herein at predetermined times of day or dynamically according to the real-time operating conditions of HX 10 compared against predetermined settings and/or limits programmed into the controller or controller software.

Alternatively, or in addition, a controller connected to valve 8 may selectively enable hot gas from the discharge of compressor 1 to be injected into the two-phase refrigerant line upstream of HX 10 upon detection of ice or upon determining that conditions are projected to exist for creating ice in the water heat exchange passages of HX 10. Valve 8 may be a three-way valve. Alternatively, valve 8 may be a combination of a three-way passage (i.e., a T-joint) and a two-way or one-way valve. When the claims recite a “three-way valve” such a recitation is hereby defined to encompass both of a three-way valve and a T-joint with a two-way or one-way valve.

Any of the one or more controllers described herein may be connected to one or more CPU's, memory, data buses, displays, user interfaces, and software configured to respond to and/or carry out computer commands.

Any of the features described with reference to FIGS. 1 to 15 may be combined into a single embodiment, even if not simultaneously shown in a single Figure.

While specific embodiments have been described in detail, it will be appreciated by those skilled in the art that various modifications and alternatives to those details could be developed in light of the overall teachings of the disclosure. Accordingly, the disclosure herein is meant to be illustrative only and not limiting as to its scope and should be given the full breadth of the appended claims and any equivalents thereof. 

1. A heat exchanger for exchanging heat between a first fluid and a second fluid, the heat exchanger comprising: a first inlet manifold, a first outlet manifold, a second inlet manifold, and a second outlet manifold; a plurality of first flow passages, each of the plurality of first flow passages fluidly connecting the first inlet manifold to the first outlet manifold; a plurality of second flow passages, each of the plurality of second flow passages fluidly connecting the second inlet manifold to the second outlet manifold; a first porous metallic insert disposed in at least one of the plurality of second flow passages, wherein a density of the first porous metallic insert varies in a direction of the second flow passages.
 2. The heat exchanger of claim 1, wherein the first porous metallic insert is a porous metallic mesh or a porous metallic foam.
 3. The heat exchanger of claim 2, wherein the first porous metallic insert comprises a beginning portion adjacent the second inlet manifold and an end portion between the second inlet manifold and the second outlet manifold, the beginning portion having a greater density than the end portion.
 4. The heat exchanger of claim 3, further comprising a plurality of porous metallic inserts, the plurality of porous metallic inserts comprising the first porous metallic insert; wherein each of the plurality of porous metallic inserts are disposed in at least one of the plurality of second flow passages to increase structural integrity of the second flow passages and/or improve thermal performance characteristics of the second flow passages.
 5. The heat exchanger of claim 4, further comprising: a front cover plate and a rear cover plate; a plurality of first plates disposed in an alternating arrangement with a plurality of second plates; wherein each of the plurality of first flow passages is defined between one of the first plates and one of the second plates, each of the plurality of second flow passages is defined between one of the first plates and one of the second plates, and each of the manifolds is at least partially defined by the plurality of first plates and the plurality of second plates.
 6. The heat exchanger of claim 5, wherein the front cover plate, the plurality of first plates, the plurality of second plates, and the rear cover plate are brazed, soldered, thermally bonded, diffusion bonded or chemically bonded together.
 7. The heat exchanger of claim 6, wherein each of the plurality of porous metallic inserts is brazed, soldered, thermally bonded, diffusion bonded or chemically bonded to at least one of the first and second plates.
 8. The heat exchanger of claim 7, wherein each of the plurality of porous metallic inserts is brazed, soldered, thermally bonded, diffusion bonded or chemically bonded to at least two plates selected from a group consisting of the front cover plate, the rear cover plate, the plurality of first plates, and the plurality of second plates.
 9. The heat exchanger of claim 8, wherein each of the plurality of porous metallic inserts has a beginning portion adjacent the second inlet manifold and an end portion between the second inlet manifold and the second outlet manifold, and a length between the beginning portion and the end portion, at least some of the lengths being different such that one of the plurality of porous metallic inserts is longer than at least some of the plurality of porous metallic inserts.
 10. The heat exchanger of claim 1, further comprising a second porous metallic insert disposed in at least one of the plurality of first flow passages, wherein a density of the second porous metallic insert varies in a direction of the first flow passages, wherein the second porous metallic insert is a porous metallic mesh or a porous metallic foam.
 11. The heat exchanger of claim 10, wherein the density of at least one of the first porous metallic inserts is different than the density of at least one of the second porous metallic inserts.
 12. The heat exchanger of claim 10, wherein the density of one of the second porous metallic inserts is different than the density of another of the second porous metallic inserts.
 13. The heat exchanger of claim 1, wherein the density of one of the first porous metallic inserts is different than the density of another of the first porous metallic inserts.
 14. An anti-freezing assembly comprising: (a) a heat exchanger for exchanging heat between a first fluid and a second fluid, the heat exchanger comprising: a first inlet manifold, a first outlet manifold, a second inlet manifold, and a second outlet manifold; a plurality of first flow passages, each of the plurality of first flow passages fluidly connecting the first inlet manifold to the first outlet manifold; a plurality of second flow passages, each of the plurality of second flow passages fluidly connecting the second inlet manifold to the second outlet manifold; (b) a heater encompassing the first inlet manifold or the first outlet manifold.
 15. The assembly of claim 14, wherein the heater encompasses only a lower portion of said manifold.
 16. The assembly of claim 14, wherein the heat exchanger comprises: a front cover plate and a rear cover plate; a plurality of first plates disposed in an alternating arrangement with a plurality of second plates; wherein each of the plurality of first flow passages is defined between one of the first plates and one of the second plates, each of the plurality of second flow passages is defined between one of the first plates and one of the second plates, and each of the manifolds is at least partially defined by the plurality of first plates and the plurality of second plates.
 17. The assembly of claim 16, wherein the heater encompasses only some of the plurality of first plates and the plurality of second plates.
 18. The assembly of claim 14, further comprising a controller and a pair of fluid sensors configured and arranged to detect a pressure or temperature of the first fluid or the second fluid, the pair of fluid sensors being in operative communication with the controller.
 19. The assembly of claim 18, wherein the controller is configured to activate the heater based on the detected pressure or temperature.
 20. The assembly of claim 19, wherein the controller is configured to activate the heater to heat the plurality of first plates closest to the rear cover plate to a greater extent than the plurality of first plates closest to the front cover plate.
 21. The assembly of claim 19, wherein the controller is configured to activate the heater to emit a greater amount of heat near the first outlet manifold and a lesser amount of heat near the first inlet manifold.
 22. The assembly of claim 19, wherein the controller is configured to activate the heater based on the detected pressure or temperature indicating a presence of ice disposed in the heat exchanger.
 23. A heat exchanger for exchanging heat between a first fluid and a second fluid, the heat exchanger comprising: a first inlet manifold, a first outlet manifold, a second inlet manifold, and a second outlet manifold; a plurality of first flow passages, each of the plurality of first flow passages fluidly connecting the first inlet manifold to the first outlet manifold; a plurality of second flow passages, each of the plurality of second flow passages fluidly connecting the second inlet manifold to the second outlet manifold; wherein the first inlet manifold has a variable cross-sectional area.
 24. The heat exchanger of claim 23, further comprising: a front cover plate and a rear cover plate; a plurality of first plates disposed in an alternating arrangement with a plurality of second plates; wherein each of the plurality of first flow passages is defined between one of the first plates and one of the second plates, each of the plurality of second flow passages is defined between one of the first plates and one of the second plates, and each of the manifolds is at least partially defined by the plurality of first plates and the plurality of second plates; wherein the cross-sectional area of the first inlet manifold is taken across a series of reference planes parallel to the plurality of first plates.
 25. The heat exchanger of claim 24, wherein the cross-sectional area of the first inlet manifold decreases along a direction extending from the front cover plate to the rear cover plate, such that a cross-sectional area of the first inlet manifold closest to the front cover plate is greater than a cross-sectional area of the first inlet manifold closest to the rear cover plate.
 26. The heat exchanger of claim 25, further comprising an inclined insert disposed in the first inlet manifold, the inclined insert being shaped such that the inclined insert is flush against each of the plurality of first and second plates.
 27. The heat exchanger of claim 25, wherein each of the first plates comprises a first aperture at least partially defining the first inlet manifold, wherein the first aperture of the first plate closest to the front cover plate is larger than the first aperture of the first plate closest to the rear cover plate.
 28. The heat exchanger of claim 27, wherein each of the second plates comprises a second aperture at least partially defining the first inlet manifold, wherein the second aperture of the second plate closest to the front cover plate is larger than the second aperture of the second plate closest to the rear cover plate.
 29. The heat exchanger of claim 24, wherein at least some of the first flow passages and at least some of the second flow passages are defined by corrugations in the first and second plates, wherein at least some of the corrugations in the first and second plates include a variable corrugation pattern comprising at least one of a variable corrugation angle of attack, a variable corrugation density, and a variable corrugation width.
 30. The heat exchanger of claim 24, wherein at least one of the first inlet manifold and the first outlet manifold are coextensively positioned with a perimeter of the heat exchanger.
 31. An anti-freezing assembly comprising: (a) heat exchanger for exchanging heat between a first fluid and a second fluid, the heat exchanger comprising: a first inlet manifold, a first outlet manifold, a second inlet manifold, and a second outlet manifold; a plurality of first flow passages, each of the plurality of first flow passages fluidly connecting the first inlet manifold to the first outlet manifold; a plurality of second flow passages, each of the plurality of second flow passages fluidly connecting the second inlet manifold to the second outlet manifold; a first porous metallic insert disposed in at least one of the plurality of second flow passages, a density of the first porous metallic insert varying in a direction of the second flow passages; wherein the first inlet manifold has a variable cross-sectional area; (b) a heater encompassing the first inlet manifold or the first outlet manifold. 